Many golf games are lost on the putting green. This is because many golfers are able to satisfactorily drive or chip the ball onto the green, only to take too many putting strokes in finally sinking the ball. In recent years it has been suggested that improved putting accuracy can be obtained by increasing the club head moment of inertia and aligning the striking point (the point where the club head strikes the ball, also known as the "sweet spot") with the center of gravity of the club head. When the club head strikes the ball away from the head's center of gravity, a moment (also called a torque) is imparted on the club head around the center of gravity. The magnitude of this moment is the impact force multiplied by the distance between the impact point and the center of gravity. This force acts to twist the club such that the face is no longer perpendicular to intended line of travel of the putting stroke, thereby causing the golf ball to be pushed by the club head in a nonintended direction and reducing accuracy.
The magnitude of this misdirected force can be reduced by minimizing the distance between the sweet spot and center of gravity (i.e. aligning the sweet spot with the center of gravity). An example of prior art that typifies this method is U.S. Pat. No. 5 078 398. However, simply aligning the sweet spot with the center of gravity alone will not always improve accuracy because every time a miss-hit occurs (a miss-hit is when the ball is struck away from the sweet spot) the twisting force will be present. The impacts of this force can be minimized by increasing the club head moment of inertia. Inertia is the physical property of a body in motion to resist change. Moment of inertia is a measurement of this property. The larger a club head's moment of inertia, the less it will be affected by the force generated from striking the ball away from the center of gravity. These effects can be described by the following equations where angular acceleration is a measure of the club head twisting motion. EQU Torque=(F) (d) EQU Angular Acceleration=(F)(d)/(Moment of Inertia)
where:
F=Impact force PA0 d=distance between strike point and center of gravity.
The amount of club head inertia is governed by the weight of the club head and the position of that weight relative to the club head center of gravity.
Many prior putters, U.S. Pat. Nos. 5,058,895 and 4,999,000 for example, have increased moment of inertia by adding peripheral weighting using high density materials. However, there is a limit to the amount and position of the weight that can be added. As the putter gets larger and heavier it loses "feel". Feel is the golfer's ability to control the impact force with the ball and the feedback the club gives the golfer about the quality of the stroke. These limits are characterized by the majority of commercially available putters having a face length of 5.5 inches or less and a weight between 280 and 320 grams.
Therefore it becomes imperative to shape the club head to maximize moment of inertia within total club head weight and size restraints. Herein lies one advantage of this invention over prior art. Described herein is a club head with increased moment of inertia which is achieved by tailoring the shape of the striking face. No prior art has tailored the club face of a putter to increase moment of inertia. The closest example of prior art is U.S. Pat. No. 4,828,265 where the face of a driver is shaped to increase club head speed by increasing dynamic pressure at the rear of the club.
Another problem encountered during putting is grounding the putter head into the green short of the ball. A normal putting stroke is characterized by keeping the wrist and arms rigid and pivoting through the shoulders. The distance from a point centered between the shoulder (center point of the arc of the putting stroke) and the sole or bottom of the putter is the radius of the putting stroke. For the average golfer this distance is approximately 48 inches. If a golfer drops his shoulders just a 0.10 inch during a putting stroke, the putter head will impact the ground 3.1 inches behind the intended point of contact with the ball (commonly known as scuffing or grounding the putter). Various methods of reducing the impacts of grounding the club have been advanced, including units which provide rollers to reduce friction, units to vertically align the sweet spot, units with soles configured to reduce the effects of grounding, and units with runners protruding from the sole.
U.S. Pat. No. 3,680,868 is typically of putters with rollers to reduce friction. U.S. Pat. No. 4,832,344 presents a sole protrusion as a means to vertically align the sweet spot of the club and reduce friction with the ground. U.S. Pat. No. 3,815,921 shows a protrusion from the sole as a means to reduce the divot on a driver. However, the protrusions on both these patents are too abrupt to effectively reduce the adverse effects of grounding the club head. U.S. Pat. No. 1,531,821 has two curved runners protruding from the sole to reduce grounding while U.S. Pat. No. 4,722,528 uses a curved leading edge. A curved surface by definition limits the amount of surface area that comes in contact with the ground, so while these designs will reduce the effects of grounding the club head over a sharp leading edge, they are not as effective as a flat surface critically aligned in the arc of the putting stroke as embodied in this invention.